An electrophotographic printer prints an image on media, such as sheets of paper, from toner contained in a toner cartridge. A developer roller or sleeve is mounted within the toner cartridge in proximity to a photoconductive drum. The photoconductive drum is charged, and a laser scans the charged photoconductive drum with a laser beam to discharge the surface and form a latent image thereon. The developer roller attracts statically charged toner from the toner container. Toner is transferred from the developer roller to the photoconductive drum to develop the latent image formed on the photoconductive drum. The developed image is then transferred to statically charged sheets of media. The sheets are fed through a heated fuser assembly, where the heat fixes the visible image.
Sheets of narrow media, such as envelopes, are aligned with a reference edge in the feed path of the printer. Because the narrow sheets do not extend across the full width of the feed path, the consecutive printing of several sheets of narrow media creates a temperature imbalance in the fuser assembly. The sheets of media, when fed past the fuser assembly to fuse the image to the sheets, remove heat therefrom. Since sheets of narrow media do not extend fully across the width of the fuser assembly, the portion of the fuser assembly away from the reference edge, where the narrow media do not contact the fuser assembly, becomes hotter than the portion adjacent the reference edge, where the narrow media contact the fuser assembly. The fuser assembly can overheat so much after printing several consecutive sheets of narrow media that it becomes damaged.
One proposed solution to the problem of the overheating in a fuser assembly with a hot roller has been to make the fuser roller out of very thick material, so that the heat diffuses more evenly across the entire width. This has been unsatisfactory, as the cost of a thick fuser roller is high. This solution, of course, is not applicable to a fuser assembly with a fuser belt.
A second proposed solution to the problem of the overheating of the fuser assembly has been the insertion of gaps between the sheets of narrow media. Inter-sheet gaps permit the fuser assembly to equilibrate between sheets. However, this solution has also been unsatisfactory, as the insertion of inter-sheet gaps for all sheets of narrow media dramatically reduces the throughput of the printer.
A third proposed solution to the problem of the overheating of the fuser assembly has been to reduce the operating temperature of the fuser assembly and the transport speed. Consequently, all the sheets of media, regardless of width, are fed past the fuser assembly at a very slow speed, so that enough heat is transferred to the media to fuse the image thereto. However, this solution has also been unsatisfactory, as the slow feeding speed for all the sheets of media severely reduces the throughput of the printer.